1. Field of the Invention
The present invention relates to a radio wave receiver that detects a reception signal received by an antenna and outputs a detection signal, a radio wave reception integrated circuit, a wave clock equipped with the radio wave receiver, and a repeater.
2. Description of Related Art
A standard radio wave including time data, that is, a time code, is sent in some countries (for example, Germany, England, Switzerland, Japan, etc.). In Japan, two transmitting stations, located in Fukushima and Saga prefectures, send out standard radio waves having frequencies of 40 kHz and 60 kHz, respectively. The time code included in a standard radio wave is sent out on a frame basis with a cycle of 60 seconds, for every update of a minute digit of the accurate time, that is, for every one minute.
There has been known a so-called wave clock that receives such a standard radio wave to thereby correct the current time data. An actual reception signal received by the wave clock is a signal in which the standard radio wave sent from a transmitting station is mixed (superposed) with noise signals, such as radio waves generated in external devices or inside the clock. The mixing of noise signals causes difficulty in reproducing the time code included in the standard radio wave, and deteriorates reception sensitivity. In order to avoid this, there have been proposed various methods for removing the noise signals mixed in the reception signal.
It is generally known, for example, to use a filter to remove noises when the received radio wave is detected. However, a filter has a certain pass band, and thus also allows passage of noise components in the vicinity of the frequency of the radio wave that is expected to pass therethrough. Further, the narrower the pass band of a filter is, the more likely a delay time is generated, which causes adverse effect on the signal processing performed thereafter. It is also known to shield a digital circuit acting as a noise source. There is also known a method in which the operation of a display circuit generating noise is suspended when the standard radio wave is received.
Generally, noise signal energy accumulated in an antenna produces a bad influence not only on a wave clock that receives a standard radio wave, but also on radio wave receivers that receive radio waves. For example, when an antenna receives a pulse-shaped noise signal, a part of the noise signal energy is accumulated in the antenna. This energy produces a signal (attenuation signal) which has the same frequency as a tuning frequency of the antenna, and is attenuated in a fairly long term relative to a generation time of the pulse acting as the noise. The larger amount of noise, that is, the larger accumulated energy makes the damping time of the damping signal longer.
Accordingly, when the antenna receives a signal mixed with a noise signal, waveform deterioration occurs due to the mixing of the noise signal, and additionally, the antenna outputs a composite signal mixed with an attenuation signal caused by the noise signal energy accumulated in the antenna (accumulated energy), that is, a signal having long lasting influence of the noise signal.